Use of conductive carbon black/graphite mixtures for the production of low-cost electronics

ABSTRACT

The invention relates to conductive polymer solutions which can be employed for the production of organic electronic components. To this end, particles of carbon black and graphite are used in the form of microplatelets in polymer solutions.

The invention relates to conductive polymer solutions, which can be employed for the production of organic electronic components.

The production of low-cost polymer electronics by printing is being continuously developed following conventional techniques, such as are employed, for example, in graphical industries. Significant disadvantages, however, arise, because on the one hand only a drastically increased resolution of the structures can provide microelectronic components and on the other hand a layer quality is demanded without which no electrical contacts or conductor tracks are at all possible.

To this end, printable inks are being developed in which the conductive polymers are readily soluble, but these substances are only soluble within narrow limits because of their rheological properties such as viscosity, adhesion, and wetting power und thus, when printed, still do not satisfy the requirements which are placed on the structure and layer quality.

Polymer solutions are known which can be rendered conductive by addition of carbon black or graphite. A mixture of carbon black particles and graphite particles is also known. The description thereof demonstrates how these mixtures can be advantageously employed for the construction of organic circuits. Other materials which improve the functionality of the layers can, of course, also be added to these mixtures, for example PANI or PEDOT.

In the case of the carbon black/graphite-filled polymer solutions, there are in this respect fewer problems, because these are variably printable within a larger concentration range in solution than the pure polymer solutions. Nevertheless, these solutions are not employed for the printing of polymer electronics, because the hard particles in the carbon black/graphite polymer solutions cause local damage to the microelectronic component and/or to the printing machine.

It is the object of the present invention to modify the particles of the carbon black/graphite particles in the polymer solutions in such a way that solutions result which cause damage neither to the components nor to the printing machines.

The invention relates to the use of a polymer solution filled with a carbon black/graphite mixture for the production of electronic components, in which solution the particles of carbon black and graphite are present substantially in the form of microplatelets.

Embodiments of the invention are evident from the subclaims.

Preferably, the method serves to construct organic electronic components, such as, for example, organic transistors and circuits containing same, organic diodes, organic-based capacitors, organic photovoltaic cells, organic sensors and actuators, and combinations thereof.

According to one embodiment, microplatelets are employed which are present in point-free form.

According to another embodiment of the invention, polymer solutions are employed which have a solids content of from 15 to 60% by weight, preferably from 20 to 45% by weight, and more preferably from 34.5 to 41% by weight.

The viscosity of the solutions used can vary greatly; both resins (viscosities between 20,000 and 40,000 mPa.s) and liquids (viscosities between 800 and 3600 mPa.s) can be employed, the term “solution” only relating to the fact that one component present is dissolved in another. The polymer solutions in question here can be liquid, gelatinous, solid or resinous, the addition of the carbon black/graphite particles again having an influence on the viscosity.

The choice of the solvent depends on the printing and/or drying properties to be achieved.

The polymer solutions containing microplatelets are highly suitable for use in low-cost microelectronics. The advantage of the polymer solutions resides in the fact that they not only provide satisfactory electrical functionality of the microelectronic component, but they also combine good processability, especially as regards the printing properties, with wide variability of the concentration of the particles of carbon black and graphite.

Preferably, carbon black/graphite-filled polymer solutions are employed which have been developed by Acheson Colloids Company (www.achesonindustries.com) for medical electrodes, battery casings, rubber resins and the like.

From the product range of Acheson materials, the type “Electrodag® PF-407A”, a known screen printing material which is not conceived for use in the microelectronics field, is employed for the pad printing of vias and gate electrodes. The material showed itself to be stable and functional in individual polymer field-effect transistors up to and including ring oscillator switching circuits.

Furthermore, promising intaglio printing tests for source/drain electrodes have been performed using “Elektrodag® 109”.

The invention discloses ready-to-print polymer solutions which can be employed for the production of polymeric microelectronic components. 

1. A method of using a polymer solution filled with a mixture of carbon black and graphite for the production of an electronic component, in which solution the particles of carbon black and graphite are present substantially in the form of microplatelets.
 2. A method as defined in claim 1, wherein said polymer solution also contains additives such as PEDOT and/or PANI.
 3. A method as defined in claim 1 or claim 2, wherein the production of said electronic component comprises at least one printing operation.
 4. A method as defined in any one of claims 1 to 3 for the construction of organic electronic components, such as organic transistors and circuits containing 1g same, organic diodes, organic-based capacitors, organic photovoltaic cells, organic sensors and actuators, and combinations thereof.
 5. A method as defined in any one of the previous claims, wherein the solids content of the particles of carbon black and graphite in said solution is between 15 and 60% by weight.
 6. A method as defined in any one of the previous claims, wherein the particles of carbon black and graphite are present as microplatelets in point-free form. 